The present invention generally relates to an apparatus and a method for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling and more particularly, relates to an apparatus and a method for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling by covering the polishing pad with a circular disc equipped with a moisture retention means and a fastening means.
Apparatus for polishing thin, flat semi-conductor wafers is well known in the art such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. A CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devises on the wafer. A wafer is xe2x80x9cplanarizedxe2x80x9d or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A perspective view of a typical CMP apparatus is shown in FIG. 1A. The CMP apparatus 10 consists of a controlled mini-environment 12 and a control panel section 14. In the controlled mini-environment 12, typically four spindles 16, 18, 20, and 22 are provided (the fourth spindle 22 is not shown in FIG. 1A) which are mounted on a cross-head 24. On the bottom of each spindle, for instance, under the spindle 16, a polishing head 26 is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head 26 with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head 26 is moved longitudinally along the spindle 16 in a linear motion across the surface of a polishing pad 28. As shown in FIG. 1A, the polishing pad 28 is mounted on a polishing disc 30 rotated by a motor (not shown) in a direction opposite to the rotational direction of the polishing head 26.
Also shown in FIG. 1A is a conditioner arm 32 which is equipped with a rotating conditioner disc 34. The conditioner arm 32 pivots on its base 36 for conditioning the polishing pad 38 for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad 28, 38 and 40 are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head 24 rotates 90xc2x0 clockwise to move the wafer just loaded into a polishing position, i.e. over the polishing pad 28. Simultaneously, a polished wafer mounted on spindle 20 is moved into the head clean load/unload station for unloading.
A cross-sectional view of a polishing station 42 is shown in FIGS. 1B and 1C. As shown in FIG. 1B, a rotating polishing head 26 which holds a wafer 44 is pressed onto an oppositely rotating polishing pad 28 mounted on a polishing disc 30 by adhesive means. The polishing pad 28 is pressed against the wafer surface 46 at a predetermined pressure. During polishing, a slurry 48 is dispensed in droplets onto the surface of the polishing pad 28 to effectuate the chemical mechanical removal of materials from the wafer surface 46.
An enlarged cross-sectional representation of the polishing action which results from a combination of chemical and mechanical effects is shown in FIG. 1C. The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is than regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
Referring now to FIG. 2A, wherein a simplified plane view of the CMP apparatus 10 is shown. In the apparatus 10, a polishing chamber 52 houses a cross member 54 equipped with four spindles 16xcx9c22 (shown in ghost lines) . The spindles 16xcx9c22 are normally connected to a polishing head 26 through a rotatable shaft (not shown).
A plane view of the CMP apparatus 10 is shown in FIG. 2B illustrating three polishing pads 92,94,96 and a conditioner arm 82. Polishing pads 92,94 and 96 are also shown without the polishing heads in place. It should be noted that for each of the polishing pad positions, i.e. for each of 92,94 and 96, a conditioner arm 82 is utilized for the in-situ conditioning of the respective polishing pads.
A slurry composition is a material that easily dries and accumulates after contacting dry air. When slurry is left on the surface of the process equipment, i.e. on the surface of the polishing pads while the machine is idling during maintenance, it will dry and accumulate to become a source of particle contamination for the wafers that are processed in the polishing chamber. Solid particles easily form on the polishing pad to cause macro-scratch on the wafer surface. Slurry particles may also become sources of particle contamination for the wafer surface and for the chamber environment. It is therefore highly desirable that particle contaminants resulting from dry slurry to be avoided or eliminated.
It is therefore an object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling that can be utilized to eliminate the drawbacks or shortcomings of the conventional chemical mechanical polishing apparatus.
It is another object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling which is constructed of a circular disc having a protruded top portion.
It is a further object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling which is constructed of a circular disc made of a substantially transparent material for covering the polishing pad.
It is another further object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling which is constructed of a substantially transparent circular disc having a diameter sufficiently large to cover a surface area of a polishing pad.
It is still another object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling which is constructed of a circular disc having a peripheral edge for overlapping a periphery of a polishing pad when the disc is positioned on top of the pad.
It is yet another object of the present invention to provide an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling which is constructed of a circular disc in two halves that can be mounted on a polishing pad in a clam-shell configuration.
It is still another further object of the present invention to provide a method for preventing drying of a polishing pad in chemical mechanical polishing during machine idling by first providing a first half and a second half of a circular disc and then mounting the two halves on a polishing pad in a clam-shell construction.
It is yet another further object of the present invention to provide a method for preventing drying of a polishing pad in chemical mechanical polishing during machine idling by first providing a circular disc and then wetting a moisture retention means mounted in the disc before positioning the disc on top of a polishing pad with the moisture retention means contacting the pad surface.
In accordance with the present invention, an apparatus and a method for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling are provided.
In a preferred embodiment, an apparatus for retaining moisture on a polishing pad in chemical mechanical polishing during machine idling can be provided which includes a first half and a second half of a circular disc, each having a protruded top portion and a peripheral edge extending downwardly in a direction perpendicular to a plane of the circular disc when the two halves are assembled together. The circular disc has a diameter sufficiently large to cover a surface area of a polishing pad with the peripheral edge of the circular disc overlaps a periphery of the polishing pad; a fastening means on an outer surface of the first half and the second half of the circular disc for assembling the two halves together; and a moisture retention means on an inner surface of the first half and the second half of the circular disc for providing a moisturizing environment to the surface area of the polishing pad.
In the apparatus for preventing drying of a polishing pad in chemical mechanical polishing during machine idling, the protruded top portion of the circular disc is off-centered relative to a center of the polishing pad, the protruded top portion of the circular disc being shaped to accommodate a polishing head mounted over and juxtaposed to the polishing pad, the protruded top portion of the circular disc being shaped further to accommodate a polishing head mounted in an operating position for engaging the polishing pad. The first half and the second half of the circular disc may be fabricated of a material that has a transparency sufficient for visual observation. The apparatus may further include a fastening means provided on an outer surface of the first half and the second half of the circular disc that includes a hook-and-loop means, or an adhesive means. The moisture retention means provided on the inner surface of the first and second halves may include bristle means for retention of water therein. The moisture retention means may further include a cellulosic material for retention of water therein. The first half and the second half may be joined together at one end in a clam-shell configuration.
The present invention is further directed to a method for preventing drying of a polishing pad in chemical mechanical polishing during machine idling which can be carried out by the operating steps of first providing a first half and a second half of a circular disc, each having a protruded top portion and a peripheral edge portion extending downwardly in a direction perpendicular to a plane of the circular disc when the two halves are assembled together. The circular disc has a diameter sufficiently large to cover a surface area of a polishing pad with the peripheral edge of the circular disc overlapping a periphery of the polishing pad, a fastening means on an outer surface of the first half and the second half of the circular disc for assembling the two halves together, and a moisture retention means on an inner surface of the first half and the second half of the circular disc for providing a moisturizing environment to the surface area of the polishing pad; wetting the moisture retention means with water; and positioning the first half and the second half of the circular disc on the polishing pad with the moisture retention means contacting the pad.
The method for preventing drying of a polishing pad in chemical mechanical polishing during machine idling may further include the step of fastening the first half and the second half of the circular disc together by a fastening means, such as by a hook-and-loop means or an adhesive means. The method may further include the step of spraying water onto the moisture retention means prior to the positioning step, or the step of providing the moisture retention means in a brush, a sponge or a cellulosic material. The method may further include the step of providing the first half and the second half of the circular disc in a material that has a transparency sufficient for visual observation. The method may further include the step of fastening the first half and the second half of the circular disc together on the polishing pad forming a clam-shell structure.